Functions for allocating/freeing memory of pointer-arrays

double **double_p_alloc(size_t nr_of_double_p)
double **double_p_free(double **ptr, size_t nr_of_double_p)
char **char_p_alloc(size_t nr_of_char_p)
char **char_p_free(char **ptr, size_t nr_of_char_p)

These allocation functions will allocate memory for an array of pointer of the specific type. The array will have place for nr_of_...pointer. These functions will return a NULL-pointer if alloction fails, too. The free functions work as the one described above. Pointer arrays are initialized with NULL pointers by the alloc functions.